Commercial calcium cyanamide (CaNCN) is actually a mixture of several components formed during or remaining after production of the desired calcium cyanamide compound. Additional components found in commercial calcium cyanamide include calcium oxide (CaO), calcium carbide (CaC2), graphite carbon (C), dicyandiamide [(HNCN)2] and oxides of iron, aluminum, and silicon.
Typically, for one reason or another, commercial calcium cyanamide is treated to alter the form of cyanamide or remove components remaining after manufacture. For example, because calcium cyanamide is a slow acting fertilizer that is sparingly soluble in water, it is often factory converted to water-soluble molecular cyanamide (H2NCN), which is faster acting and a higher analysis source of nitrogen. In this process, calcium cyanamide is forced to dissolve in water by precipitation of calcium ions (Ca2+) as calcium carbonate (CaCO3) and by acidification to convert initially formed cyanamide ions (NCN2−) into acid cyanamide ion (HNCN−) and then into molecular cyanamide, which predominates at a pH of 4.5-5.5. Insoluble calcium carbonate and graphite carbon, which may be entrained in the calcium carbonate, are then removed by filtration. The resulting solution must be kept cool, for example, refrigerated, because it is unstable above about 70° F.
Calcium oxide and calcium carbide also are removed during the process used to provide molecular cyanamide from calcium cyanamide. Calcium oxide is converted to calcium hydroxide and further into calcium carbonate. In the case of calcium carbide, the carbide ion reacts with water to form acetylene that is lost as a gas to the atmosphere. Thus, many of the components originally in commercial calcium cyanamide are converted, removed, or lost. Since the various components of commercial calcium cyanamide also may benefit plants and soils, methods and compositions that maximize the utility of all of its various components are desirable.
A. Calcium
Calcium ions (Ca2+) are present in most organic matter and are necessary for many enzymatic reactions, including those that facilitate energy use by living organisms. Furthermore, calcium ions aid in soil reclamation by flocculating soil and permitting water percolation. Additionally, calcium tends to enhance the breakdown of organic matter through these and other actions.
While calcium ions are abundant in nature in naturally occurring limestone (calcium carbonate, CaCO3), they are not readily available for uptake because of the relative insolubility of calcium carbonate. From this is seen the need to stabilize calcium ions in soluble form to enhance the speed of calcium uptake into organic matter, both living and dead, to aid plant growth and soil reclamation.
Completely ignored to this date is calcium cyanamide's potential as a source of stabilized Ca2+ that can rapidly enter plants and flocculate soil. While promotional literature does mention calcium cyanamide as a possible soil amendment, unstabilized it is no more useful than inexpensive mined lime (CaCO3). However, if the soluble forms of calcium could be stabilized, it would provide added value to calcium cyanamide.
Stabilizing soluble calcium ions at the immediate first hydrolysis step during the production of molecular cyanamide from commercial calcium cyanamide has been overlooked. Typical descriptions of the hydrolysis of calcium cyanamide indicate conversion directly to molecular cyanamide and calcium carbonate. Furthermore, some prior hydrolysis schemes ensure complete loss of soluble calcium through CO2 enrichment during aerobic hydrolysis, to provide calcium free, acid stabilized molecular cyanamide, or soluble acid cyanamide salts. Such processes leave lime (CaCO3) and dicyandiamide (DiCy), formed as the initial calcium cyanamide solution is acidified through the pH range of 8-10, blackened by graphite carbon (C), in huge, now environmentally suspect piles, behind calcium cyanamide factories. Given the huge energy costs of initial calcium cyanamide production and subsequent analog production costs, it is unfortunate that a valuable nutrient such as calcium is left behind in piles of black lime for the sake of obtaining only nitrogen fertilizer from calcium cyanamide. The wastefulness of this practice is highlighted in that the major portion of commercial CaNCN is calcium. It is therefore desirable to stabilize and deliver the calcium component of calcium cyanamide for decomposition (composting) enhancement, odor and organism inhibition, plant nutrition, and soil flocculation.
B. Nitrogen
Nitrogen, in its molecular form (N2) comprises approximately 78% of the earth's atmosphere. Nitrogen is a component of all proteinaceous matter found in living organisms, but only a few organisms (such as nitrogen-fixing bacteria) are able to directly capture atmospheric nitrogen and add it to the biosphere.
Proteinaceous matter, contained in dead and decaying organic matter and additionally in the excreta of animals represents a vast potential source of nitrogen for growth of living organisms. However, in proteinaceous form, nitrogen is insoluble and unavailable to living organisms except through the action of decomposers, which release nitrogen in the forms of gaseous NH3 and leachable NH4+, NO2−, and NO3−. These forms can be utilized by plants and allow nitrogen to reenter the living biosphere.
In many instances the rate at which nitrogen becomes available from decomposing (composting) organic matter is insufficient to provide rates of plant growth that are desired by modern agriculture. Instead, synthetic nitrogen fertilizers have been utilized, leaving huge, unused stores of environmentally suspect animal excreta. Thus, there exists a need for an environmentally sound method that increases the rate at which nitrogen becomes available to plants from decomposing organic matter.
Modern agriculture supplements plant available nitrogen by using high analysis nitrogen fertilizers, such as inexpensive urea, ammonia, ammonium compounds, and nitrates. Concurrently, use of calcium cyanamide, the first commercially available high analysis fertilizer, has declined due to the high cost of its manufacture and to the handling, shipping, and phytotoxicity problems it poses.
While modern, low-cost, fast-acting high analysis nitrogen fertilizers can provide abundant nitrogen for rapidly growing plants, their use has produced some undesirable consequences, such as leaching of nitrates into groundwater and losses of volatile ammonia to the atmosphere. These are also problems associated with composting and applying animal excreta directly to soils. Thus, it is desirable to provide compositions and methods that promote release of nitrogen from proteinaceous materials, yet slow its loss to the atmosphere and from soil. It is also desirable to provide compositions and methods that stabilize and extend the residence time of high nitrogen analysis fertilizers in the plant root zone.
C. Calcium and Nitrogen
Plants deficient in calcium but provided with an abundance of nitrogen are prone to parasitic organisms. Conversely, plants with high ratios of calcium-to-nitrogen resist parasitic organisms. It is also known that it is difficult to provide plants with calcium in direct proportion to the rate at which they can absorb soluble nitrogen forms, even if calcium and nitrogen are provided as water-soluble calcium nitrate (CaNO3). Slow acting calcium sprays and expensive chelated forms of calcium have been reported not to cure calcium deficiencies observed during intensive nitrogen demanding vegetable production in California (Crop Notes, UC Extension, Salinas, Calif., July 2000). Therefore, it would be desirable to have compositions and methods that stabilize soluble calcium and promote calcium uptake by plants in proportion to nitrogen uptake, thereby conferring parasite resistance to the plants.
D. Calcium Cyanamide (CaNCN)
Calcium cyanamide which comprises 44% calcium and 24% nitrogen, was first made in the late 1800s, as part of a search for a high analysis nitrogen source for industry and agriculture to replace low analysis (1-<12%) excreta deposits. It is produced in 1000 to >3,000° C. electric arc furnaces by burning black coal and white limestone in the presence of atmospheric nitrogen. Energy costs represent the bulk of calcium cyanamide production costs.
Because calcium cyanamide is slow acting, one application at a rate of 1000 to 2000 lbs/acre lasts all growing season long. However, when calcium cyanamide is applied at these typical season long rates, particularly in cool and or dry conditions, it is necessary to delay planting until the high concentrations of plant penetrating initial hydrolysis products of calcium cyanamide, which are toxic to seeds and seedlings (phytotoxic), dissipate. Furthermore, because calcium cyanamide in its noxiously dusty irregular granule form is difficult to calibrate, its application may be haphazard so that one part of a field may be ready for planting while others exhibit persistent phytotoxicity. The phytotoxic characteristics of calcium cyanamide also make even repeated dry applications at lower rates impractical.
The observation that calcium cyanamide exhibits phytotoxicity led to its use as an herbicide. However, its use as an herbicide has largely been discontinued in favor of modern herbicides.
For the reasons above, use of dry calcium cyanamide has decreased, and presently it is no longer used in the United States. Worldwide, its use is largely restricted to rice cultivation, where hot, wet conditions quickly degrade and remove other nitrogen fertilizers, such as urea, from the soil.
Calcium cyanamide is more typically converted to faster acting and higher analysis forms of nitrogen. For example, calcium cyanamide may be aerobically hydrolyzed in the presence of carbon dioxide to provide calcium free urea (42% N). Other high analysis nitrogen forms which are produced from calcium cyanamide include calcium free, dicyandiamide ((HNCN)2, 66% N) and molecular cyanamide (H2NCN, 66% N). These forms have found use in both agriculture and the production of many of today's industrial polymer chemicals and medicines. However, plant beneficial calcium is not a part of these products.
It would be a benefit to provide compositions and methods that exploit the slow acting nature of calcium cyanamide yet provide immediately available plant nitrogen without phytotoxic consequences. It also would be a benefit if such compositions and methods made it easier to calibrate applications of calcium cyanamide and facilitated repeated smaller applications throughout the growing season. Furthermore it would be an advantage if these benefits were achieved at more economical rates of application and enabled more of the components that exist in commercial calcium cyanamide to be utilized.
These benefits have been partially realized by Hartmann, as described in U.S. Pat. Nos. 5,698,004 and 5,976,212, which are incorporated herein by reference. Contrary to teachings against fertilizing plants with the initial hydrolysis products of calcium cyanamide (because of their phytotoxicity), Hartmann has worked to provide easily deliverable, stable, hydrolyzed ionic CaNCN solutions, containing plant penetrating acid cyanamide anions directly to plants. Caustic is added to such ionic solutions to maintain a pH that favors the acid cyanamide ion. The calcium cyanamide solutions taught in these prior patents are sprayable if insolubles, such as calcium carbonate and residual carbon, are retained such as by a means of filtration. Balls and clumps of calcium carbonate that entrain otherwise sprayable carbon tend to plug pumping and spraying equipment. Because carbon is also beneficial to plants and soils it would be advantageous if methods existed to prevent formation of such balls and clumps, so that more calcium remained soluble, filtration was unnecessary, and the residual insoluble carbon found in commercial calcium cyanamide could be maintained in a sprayable slurry. Furthermore, it would be a benefit if it were possible to maintain a pH favorable to acid cyanamide ions without having to add caustic to overcome the tendency of these solutions to drop in pH.
E. Urea
Urea, today, is made in approximately 75 factories worldwide with a total capacity approaching 100,000,000 tons annually. Dry, water-soluble urea is a low cost, fast acting, and easily calibrated soluble nitrogen form. However, urea is recognized to undergo rapid hydrolysis, which may lead to ammonia gas release and/or losses due to nitrate leaching. Urea and excreta hydrolysis also contribute large amounts of the greenhouse gas CO2. In fact, urea and decomposed proteinaceous animal excreta containing urea are now considered so environmentally threatening that farmers using such fertilizers have already been subject to fines and judgments ($30,000 to $300,000) for violation of clean water laws that regulate nitrates. It therefore would be desirable to provide compositions and methods that allow urea and animal excreta to be utilized as fertilizers without ammonia loss or rapid leaching of nitrates.
There are two basic prior approaches to simultaneously making urea-derived nitrogen available to plants for longer periods and reducing nitrate contamination. The first is to slow urea dissolution. The second is to slow the conversion of urea to nitrate by soil microorganisms, either by inhibiting the action of urease or inhibiting nitrification, or both.
Urea dissolution control may be accomplished by coating urea with hydrophobic substances, such as sulfur, to produce slow release granules. U.S. Pat. No. 4,081,264 to Ali exemplifies this technology. Ali describes encapsulated slow release fertilizers prepared by coating a fertilizer substrate (e.g. urea) with molten sulfur. Sulfur coated urea particles are brittle so they are often coated with a plasticizing substance, such as bitumen, to increase their mechanical strength. Finally, another coating of an inorganic material, such as talc, may be required to provide a free flowing material. While slow release granules can extend nitrogen availability throughout the growing season and reduce nitrate leaching, they are too costly for general agricultural use, especially in light of their lower nitrogen content.
Urease inhibitors serve to slow the conversion of urea to ammonium ions. Such inhibitors include phosphoric triamides, such as N-(n-butyl)thiophosphoric triamide (NBPT) (see for example U.S. Pat. No. 4,530,714). Phosphoric triamides however are difficult to handle and susceptible to decomposition. Efficient incorporation of phosphoric triamides into granular urea-containing fertilizers may be accomplished using liquid amide solvents, but use of such solvents in the granulation process increases fertilizer costs.
Nitrification inhibitors, when combined with urea, ammonia, and ammonium salt fertilizers, also can serve to reduce nitrate leaching. Known nitrification inhibitors include dicyandiamide (DD) and N-Halamine compounds. Dicyandiamide, which is made from calcium cyanamide, also functions as a nitrification inhibitor. It is however, short lived in hot soils.
While calcium cyanamide is believed to function as both a urease and nitrification inhibitor, direct addition of calcium cyanamide to urea is dissuaded because the residual calcium oxide in commercial calcium cyanamide promotes ammonia volatilization, especially under wet conditions (Nianzu et al., Fertilizer Research, 41: 19-26, 1995).
What is needed therefore are compositions and methods that make it possible to take advantage of calcium cyanamide's potential to mitigate nitrate leaching following application of urea. Furthermore it would be advantageous to provide compositions and methods that make it possible to combine commercial calcium cyanamide directly with urea, even in wet conditions, and preserve the calcium oxide component of the calcium cyanamide and/or its water dissolution products.
F. Cyanamide Dissolution and Hydrolysis Products
When calcium cyanamide first dissolves in water it produces calcium ions (Ca2+) and cyanamide ions (NCN2−) as products. The cyanamide ion is very basic and reacts with water to form the acid cyanamide ion (HNCN−). The acid cyanamide ion is amphoteric, i.e. it can act as either an acid or a base. If the acid cyanamide ion acts as an acid it will revert to the cyanamide ion, and if it acts as a base it will react to form molecular cyanamide (H2NCN). The form that cyanamide takes in solution will depend upon the pH of the solution, but molecular cyanamide is favored at pH's below 10.3, which are typical of soils. Molecular cyanamide may then undergo hydrolysis to form urea, which may further react to form ammonium ions, which may further be converted to volatile ammonia or to nitrate.
As stated previously, the acid cyanamide ion is plant and organism penetrating. Once absorbed by plants, the acid cyanamide ion lasts only 2-4 hours before it forms urea, which lasts 4-8 hours. Both acid cyanamide and urea stimulate arginine production in plants; however, cyanamide stimulates arginine production 20-times more effectively than urea. Arginine production is related to activation of both plant reproductive responses and disease and pest resistance in plants. Such activation is termed “Systemically Activated Resistance” or SAR (see for example, Kunz et. al., Zeitschrift fur Plantzen Krankheiten und Flanzenschutz, 61: 481-521, 1954; Lovatt et. al., Proceedings California Plant and Soil Conference 1992 & 1995; Wunsch et. al., Zeitshrift fur Pflanzenphysiology, 72: 359-366, 1974; and Von Fishbeck et. al., Zeitschrifi fur Planzen Krankheiten, 71: 24-34, 1964). Therefore, compositions and methods that stabilize and provide acid cyanamide ions to plants over long periods of time are desirable for producing fruitful, parasite free plants.
When CaNCN is applied at fertilizer rates, atop warm, wet soil, rapid uncontrollable aerobic hydrolysis occurs, moving initially soluble calcium to insoluble calcium forms and cyanamide ions to urea, then gaseous ammonia at that location. A need is thus seen to economically stabilize initial pre-hydrolysis soluble acid cyanamide ions and calcium ions in high dilutions so that they can rapidly percolate to target sites of choice where the ions can be absorbed by plants and aid in maintaining soil porosity.
In addition, USDA geneticists have recently succeeded in placing the Cah gene from natural soil cyanobacteria into crop plants cells to make them resistant to the phytotoxicity of acid cyanamide (HNCN) ions. This gene permits a plant to rapidly convert acid cyanamide ions to non-phytotoxic urea. Using CaNCN fertilizer as a dual-use foliar herbicide and nitrogen source is envisioned as an attractive alternative to single-use herbicides (USDA Agricultural Research/July 1998). Thus, should crop plants with the Cah gene obtain regulatory approval, a need for target site delivery of a stabilized source of acid cyanamide ions will arise.
Another product of calcium cyanamide dissolution and hydrolysis is dicyandiamide. Dicyandiamide is formed by polymerization of cyanamide in the presence of ammonia, alkaline earth hydroxides (e.g. Ca(OH)2), or other bases, and particularly at a pH between 8 and 10.
G. Calcium Carbide
Calcium carbide (CaC2), the initial product of arc furnace burning (>3,000 C) of ccal and lime, remains a residual in commercial calcium cyanamide. Hydrolyzing calcium carbide produces water-soluble acetylene gas (C2H2), which is about 50% as soluble in water as CO2 but less dense. Due to Department of Transportation regulations, the calcium carbide content of calcium cyanamide must be reduced below 0.1% before it can be shipped. Regardless, enough residual carbide exists in commercial calcium cyanamide to produce a noticeable carbide gas odor upon opening a sealed vessel of water in which calcium cyanamide has been mixed.
Acetylene itself has been implicated as a nitrification inhibitor (“Improving the Efficiency and Predictability of Biological Inhibitors to Reduce Nitrogen Losses and Enhance Flooded Rice Productivity,” Termination Report for ACIAR Special Purpose Grant, by International Fertilizer Development Center, November 1997). However, encapsulated calcium carbide (ECC), was shown to significantly affect yield over urea only when applied with urease inhibitors; otherwise, yields with urea plus ECC were similar to urea.
Because the residual calcium carbide content of calcium cyanamide is typically factory reduced for shipping by sprinkling it with water in the presence of atmospheric carbon dioxide, the soluble calcium content of commercial calcium cyanamide is effectively reduced by production of calcium carbonate. Therefore, compositions and methods that eliminate the need to remove calcium carbide prior to shipment would be desirable. Furthermore, methods and compositions that take advantage of the calcium carbide component of calcium cyanamide to provide nitrification inhibition, and/or provide an alternative to current methods of stabilizing calcium carbide for application to soils, are desirable.
H. Calcium Oxide
Calcium oxide, a by-product of calcium cyanamide production, is considered a nuisance for at least two reasons. First, calcium oxide readily absorbs carbon dioxide from the atmosphere to form calcium carbonate. Calcium carbonate, has a density that is lower than calcium oxide and therefore occupies more space than the calcium oxide from which it forms. When calcium oxide reacts to form calcium carbonate within particles of commercial calcium cyanamide, the result is an expansion that leads to cracking and noxious dusting of the calcium cyanamide product. Second, calcium oxide reacts with water to form calcium hydroxide, a strong base. During production of molecular cyanamide from calcium cyanamide, the calcium oxide component of the commercial calcium cyanamide product makes it necessary to add additional acid to lower the pH to 4.5-5.5, thus adding expense to the molecular cyanamide product.
As discussed previously, calcium oxide also is a potential source of calcium ions from commercial calcium cyanamide. Therefore, it is desirable to preserve the soluble calcium that is contained in the calcium oxide. Furthermore, as also discussed above, it is advantageous to prevent production of insoluble calcium carbonate from calcium oxide if spray application of calcium cyanamide is desired.
I. Organics
In recent years odorous “greenhouse gas” emissions, coliform bacteria, leachable nitrogen, and phosphate from concentrated animal feeding operations has become an environmental concern, both in the US and the throughout the world. Such concerns have prompted world-wide funding of livestock operations inspections for compliance with herd size and odor, disease and water nutrient level mitigation measures. For example, in the Netherlands, animal operations must account for and balance every single unit of input with output units. Aerobic composting that wastefully releases nitrogen and carbon into the atmosphere, and storage of animal wastes in vast aerobic, odorous lagoons still remain the principal available mitigation measures short of reducing herd size and suffering negative economic consequences.
Thus there appears a vast urgent need to provide an economical, practical and rapid, non-gas releasing, composting alternative to animal feeding sites. Such an alternative method of composting would desirably reduce the odor and disease causing organisms associated with animal wastes while resulting in a fertilizer composition that contains stabilized nutrients which promote sustained growth and parasite resistance in plants and serve as effective soil amendments.
J. Metals
Metals are an essential to life. However, metals are increasingly being leached below plant root zones due to the increased use of soluble, acid forming nitrogen plant foods. One solution to this problem is to apply lime to soils because many metals are less likely to leach from soils of higher pH. Lime, albeit inexpensive, requires tons per acre and considerable application expenses to achieve modest increases in soil pH. As explained earlier, lime is virtually insoluble, thus slow to release soluble calcium and pH increasing carbonate ions. Thus, lime only slowly raises soil pH, especially at depth in the soil where it is desired to immobilize metals near plant roots so that they are available to the plants. What are needed are compositions and methods that can supply metal micro-nutrients quickly to plant root zones and stabilize them in the root zone by raising the pH of the soil at depth. Because commercial calcium cyanamide contains approximately 2% oxides of the elements iron, silicon, and aluminum, it would also be advantageous to make use of calcium cyanamide as a source of these micro-nutrients while simultaneously providing for their stabilization in the soil.
Carbon dioxide and catalytic converter metal deposits from auto exhausts are apparently resulting in metal leaching into groundwater along roadsides. Acidic conditions develop along roadsides through carbon dioxide dissolution in rain water and decomposition of plant matter. These conditions foster leaching of deposited metals, some of which are toxic. For example, although lead is no longer a component of most gasoline products, lead contamination remains a problem where high concentrations of the metal were deposited in the past. Thus, there is a need to slow or prevent leaching of metals from soils along roadsides. Again, application of lime is one possible solution, but what are needed are compositions and methods that can provide metal stabilization in soils without the limitations of lime discussed previously.